1. Field of the Invention
This invention relates to gas-discharge lighting in general and, more particularly, to electronic ballast circuits used in gas-discharge lighting systems.
2. Description of the Prior Art
Gas discharge lighting, such as sodium vapor or fluorescence lighting, is used where the higher efficiency of gas discharge lighting over incandescent lighting is important, such as in office buildings where there may be thousands of lighting fixtures.
Each gas discharge lighting fixture or system has a ballast which controls the operation of one or more gas discharge lamp therein. The ballast serves to provide the correct voltage and current to the lamp when the fixture is first turned on and thereafter. The ballast is recognized as the component most needing improvement to increase the efficiency of gas discharge lighting.
The initial ballast designs were large transformers and chokes that operated at the power line frequency (e.g.,50 or 60 Hz) and were heavy and dissipated a lot of power. These were replaced with electronic ballasts that still relied on transformers for control and chokes for current limiting, but operated at higher frequencies (tens of KHz) to achieve better efficiencies, reduced weight, and smaller size (the transformers and chokes can be much smaller when operated at the higher frequencies). While the transformer-based electronic ballast is relatively simple, the control transformer may reduce the efficiency of the ballast. Moreover, transformer-based electronic ballast are difficult to design, relying on the magnetic properties of the transformer to achieve the desired voltage and current to the gas discharge lamp on startup and thereafter. Changing the transformer characteristics is an expensive, time consuming, and inexact operation, usually requiring more than two design attempts and tests to insure proper operation.
Thus, it is desirable to provide a ballast design that does not use a transformer.
Further, it is desirable to provide a ballast design that replaces a control transformer with an electronic circuit that synthesizes the function of the transformer.
Still further, it is desirable to provide a ballast design that is readily adaptable for different applications.